Add an Overview of the Framework page

docs/src/framework/README.md

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-# An Overview of Framework APIs
+# Asterinas Framework
+
+> Confucious remarked,
+> "I could follow whatever my heart desired
+> without transgressing the law."
+>
+> 子曰：
+> "从心所欲，不逾矩。"
+
+With Asterinas Framework,
+you don't have to learn the dark art of unsafe Rust programming
+and risk shooting yourself in the foot.
+You will be doing whatever your heart desired
+and be confident that your kernel will never crash
+or be hacked due to undefined behaviors,
+even if today marks your Day 1 as a Rust programmer.
+
+## APIs
+
+Asterinas Framework stands
+as a powerful and solid foundation for safe kernel development,
+providing high-level safe Rust APIs that are
+
+1. Essential for OS development, and
+2. Dependent on the use of unsafe Rust.
+
+Most of these APIs fall into the following categories:
+
+* Memory management (e.g., allocating and accessing physical memory pages)
+* Task management (e.g., context switching between kernel tasks)
+* User space (e.g., manipulating and entering the user space)
+* Interrupt handling (e.g., registering interrupt handlers)
+* Timer management (e.g., registering timer handlers)
+* Driver support (e.g., performing DMA and MMIO)
+* Boot support (e.g., retrieving information from the bootloader)
+* Synchronization (e.g., locking and sleeping)
+
+To explore how these APIs come into play,
+see [the example of a 100-line kernel in safe Rust](a-100-line-kernel.md).
+
+## Four Requirements Satisfied
+
+In designing and implementing Asterinas Framework,
+we have risen to meet the challenge of
+fulfilling [the aforementioned four criteria as demanded by the framekernel architecture](../kernel/the-framekernel-architecture.md).
+
+Expressiveness is evident through Asterinas Kernel itself,
+where all system calls,
+file systems,
+network protocols,
+and device drivers (e.g., Virtio drivers)
+have been implemented in safe Rust
+by leveraging the Framework.
+
+Adopting a minimalist philosophy,
+the Framework has a small codebase.
+At its core lies the `aster-frame` crate,
+currently encompassing about 10K lines of code
+---a figure that is even smaller than those of many microkernels.
+As the Framework evolves,
+its codebase will expand,
+albeit at a relatively slow rate
+in comparison to the OS services layered atop it.
+
+The Framework's efficiency is measurable
+through the performance metrics of its APIs
+and the system calls of Asterinas Kernel.
+No intrinsic limitations have been identified within Rust
+or the framekernel architecture
+that could hinder kernel performance.
+
+Soundness,
+unlike the other three requirements,
+is not as easily quantified or proved.
+While formal verification stands as the gold standard,
+it requires considerable resources and time
+and is not an immediate priority.
+As a more pragmatic approach,
+we will explain why the high-level design is sound
+in the [soundness analysis]()
+and rely on the many eyes of the community
+to catch any potential flaws in the implementation.